(1) Field of the Invention
The present invention relates to a process for the preparation of organic pigments having excellent dispersibility, color sharpness, gloss, coloring power, and flowability.
As is well known, organic pigments generally have a sharp color, and they are valuable as colorants for lacquers, printing inks and the like. Dispersibility, gloss, flowability, and coloring power are important as practical properties required for organic pigments.
(2) Description of the Related Art
As methods for improving the practical properties of organic pigments, there have been proposed (1) a method in which the surface of a pigment is covered with a surface active agent or a resin, (2) a method in which a substituted derivative of a pigment is incorporated in the base pigment, and (3) a method in which a pigment is converted to a processed pigment such as a paste color or master batch color.
The method (1) has a problem such that the improvement of the flowability and gloss is insufficient and the coloring power is reduced. In the method (2), since the pigment has an inherent color, application to a pigment of a different hue cannot be made, and derivatives must be prepared for respective pigments. Accordingly, the method (2) is industrially disadvantageous. In the method (3), a large electric power, much labor, and a long time are required for processing, and therefore, the manufacturing cost is high. Furthermore, since a specific vehicle or resin has to be used, the application range is limited and the method (3) does not have a sufficient general-purpose characteristic. Accordingly, none of these known methods are practically satisfactory. Moreover, each of the known methods is an ex post facto method, and substantial prevention of an aggregation of pigment particles is almost impossible. Accordingly, in any of these known methods, satisfactory results cannot be always obtained in the modification of pigments.